. Updated version of native threads for FreeBSD. This uses recently
committed enhancements to libc_r and is only suitable for very recent
versions of FreeBSD. The big benefit is that it removes almost all
the previous grovelling about in the pthreads internals.
The change only comes into effect when WITH_NATIVE_THREADS is set.
A separate Makefile commit will attempt to enforce appropriate
OSVERSION settings for using it.
Submitted by: fjoe